<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<select id="s1" onchange="dianyin()">
			<option value="中国">中国</option>
			<option value="韩国">韩国</option>
			
				
		</select>
		
		<select id="s2">
			<option>北京</option>
			<option>首尔</option>
			
		</select>
		
			
	
		
	
		
		<script>
			function dianyin(){
				if(s1.value=="中国"){
					 s2.innerHTML="<option>北京</option>"}
					
					
				else if(s1.value=="韩国"){
					s2.innerHTML="<option>首尔</option>"}
				
				
					}
		</script>
	</body>
</html>
